1. Field of the Invention
The present invention relates to a method for filtering a chemical that is used in a process of manufacturing the chemical, a lithography process, and a cleaning process.
2. Background Art
In semiconductor devices according to the conventional art, a filter that filters an impurity from a used chemical may be included (for example, see Japanese Patent Laid-Open No. 2008-72096).
For example, in a filter that is used in a process of manufacturing and refining a chemical in the conventional art, a pressure of an outlet thereof is monitored, it is determined that the filter is deteriorated when the pressure is lowered, and an exchange period of time of the filter is managed based on the determination result.
Further, in another method that manages an exchange period of time of a filter, a filtering time is monitored, and it is determined that the filter is deteriorated, if a filtering time exceeds a predetermined time.
Meanwhile, a standard pore size of the filter is determined but is not constant. For this reason, even though a hole of the filter having a small pore size is clogged by a capture, a flow rate is not lowered. As a result, a deterioration of the filter may not be monitored. Further, a chemical and an impurity pass through a relatively large hole of the filter, and the amount of impurity contained in the chemical is increased.
Accordingly, if only the method for monitoring a filtering time is used, an exchange period of time of the filter cannot be properly managed.
As such, in the method for filtering a chemical according to the conventional art, a desired chemical having a standard impurity cannot be manufactured.